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Three dimensional Particle-in-Cell (3D-PIC) simulations of electron acceleration in vacuum with radially polarized ultra-intense laser beams have been performed. It is shown that single-cycle laser pulses efficiently accelerate a single attosecond electron bunch to GeV energies. When multi-cycle laser pulses are used, one has to employ ionization of high-Z materials to inject electrons in the accelerating phase at the laser pulse maximum. In this case, a train of highly collimated attosecond electron bunches with a quasi-monoenergetic spectra is produced. A comparison with electron acceleration by Gaussian laser pulses has been done. It is shown that the radially polarized laser pulses are superior both in the maximum energy gain and in the quality of the produced electron beams.